ZEND PHP 5 Certification STUDY GUIDE

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Chapter 8 Elements of Object-oriented Design The benchmark of a good programmer, regardless of what language they work with, is their ability to apply well-known and accepted design techniques to any given situation. Design Patterns are generally recognized as an excellent set of tried-and-true solutions to common problems that developers face every day. In this chapter, we’ll focus on how some of PHP 5’s new facilities, such as proper object orientation, can make the development of pattern-driven applications easier. While the exam is not strewn with complex examples of pattern development, it does require you to have a firm grasp of the basics behind design patterns and their use in everyday applications. Design Pattern Theory As we mentioned in the previous section, design patterns are nothing more than streamlined solutions to common problems. In fact, design patterns are not really about code at all—they simply provide guidelines that you, the developer, can translate into code for pretty much every possible language. In this chapter, we will provide a basic description of some of the simpler design patterns, but, as the exam concerns itself primarily with the theory behind them, we will, for the most part, stick to explaining how they work in principle. Even though they can be implemented using nothing more than procedural code, design patterns are best illustrated using OOP. That’s why it’s only with PHP 5 that Licensed to 482634 - Amber Barrow (itsadmin@deakin.edu.au)
172 ” Elements of Object-oriented Design they have really become relevant to the PHP world: with a proper object-oriented architecture in place, building design patterns is easy and provides a tried-and-true method for developing robust code. The Singleton Pattern The Singleton is, probably, the simplest design pattern. Its goal is to provide access to a single resource that is never duplicated, but that is made available to any portion of an application that requests it without the need to keep track of its existence. The most typical example of this pattern is a database connection, which normally only needs to be created once at the beginning of a script and then used throughout its code. Here’s an example implementation: class DB { private static $_singleton; private $_connection; private function __construct() { $this->_connection = mysql_connect(); } public static function getInstance() { if (is_null (self::$_singleton)) { self::$_singleton = new DB(); } return self::$_singleton; } } $db = DB::getInstance(); Licensed to 482634 - Amber Barrow (itsadmin@deakin.edu.au) Our implementation of the DB class takes advantage of a few advanced OOP concepts that are available in PHP 5: we have made the constructor private, which effectively ensures that the class can only be instantiated from within itself. This is, in fact, done in the getInstance() method, which checks whether the static property $_singleton has been initialized and, if it hasn’t, sets it to a new instance of DB. From this point on, getInstance() will never attempt to create a new instance of DB, and instead always
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vi ” CONTENTS Operators . . . . .
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viii ” CONTENTS Delimiters . . .
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x ” CONTENTS The Factory Pattern
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xii ” CONTENTS Appendix A — Dif
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xviii ” CONTENTS study process mu
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4 ” PHP Basics Standard Tags Shor
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6 ” PHP Basics Comments Another c
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8 ” PHP Basics Another very impor
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10 ” PHP Basics You would expect
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12 ” PHP Basics ply the names of
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14 ” PHP Basics } echo ’myFunc!
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16 ” PHP Basics Arithmetic Operat
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18 ” PHP Basics $string2 = "baz";
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20 ” PHP Basics 4,294,967,296—w
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22 ” PHP Basics == Equivalence. E
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24 ” PHP Basics echo !$a; // outp
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26 ” PHP Basics Associativity Ope
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28 ” PHP Basics The code above wo
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30 ” PHP Basics true, the code in
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32 ” PHP Basics } echo $i . PHP_E
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34 ” PHP Basics i Error reporting
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38 ” Functions { } echo "Hello Wo
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40 ” Functions However, any time
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42 ” Functions Variable-length Ar
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44 ” Functions // Remove the defi
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48 ” Arrays assigns a numeric key
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50 ” Arrays $a = array (’4’ =
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52 ” Arrays } int(3) Note how the
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54 ” Arrays echo isset ($a[’a
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56 ” Arrays cope with the fact th
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58 ” Arrays If, however, all you
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60 ” Arrays $type = array(’inte
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62 ” Arrays ["b"]=> string(3) "ba
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64 ” Arrays { // Sort according t
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66 ” Arrays $cards = array (1, 2,
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68 ” Arrays $last_in = array_pop(
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70 ” Arrays want it to be compute
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74 ” Strings And Patterns Escape
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76 ” Strings And Patterns When us
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78 ” Strings And Patterns Note th
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80 ” Strings And Patterns You can
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84 ” Strings And Patterns Formatt
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88 ” Strings And Patterns b c d e
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90 ” Strings And Patterns lier in
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92 ” Strings And Patterns Sub-Exp
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94 ” Strings And Patterns [0]=> a
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98 ” Web Programming made for a P
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100 ” Web Programming Note that,
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102 ” Web Programming file (usual
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104 ” Web Programming GET or POST
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106 ” Web Programming The level o
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108 ” Web Programming UNIX timest
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110 ” Web Programming session.aut
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114 ” Object Oriented Programming
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228 ” Security if (count($results
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232 ” Security While this attack
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238 ” Streams and Network Program
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254 ” Differences Between PHP 4 a
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258 ” INDEX as stacks, 68 calcula
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260 ” INDEX constants, 14 class c
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262 ” INDEX removeAttribute(), 20
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266 ” INDEX ArrayAccess, 177 offs
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268 ” INDEX set_exception_handler
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270 ” INDEX with printf(), 87 her
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ZEND PHP 5 Certification STUDY GUIDE

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